Silicone rubbers have improved heat resistance, weather resistance, durability, releasability, and electrical properties and are formable or moldable to any desired shape. They have found a wide variety of uses as building materials, electric and electronic parts, automobile parts and business machines. Because the use of business machines is now expanding, silicone rubbers, partially because of their improved compression set, in addition to the above-mentioned properties, are now indispensable as roll materials for copying machines and printers.
Roll material require silicone rubbers of low hardness. Most often, low hardness silicone rubbers having a hardness as low as 40 or less in JIS A scale are employed. There is a demand for silicone rubber having a lower hardness. In general, low hardness silicone rubbers are obtained by reducing the vinyl group content of a predominant polymer component in a silicone rubber composition or reducing the content of silica filler therein. However, a certain limit exists when reducing the vinyl content. With too low a content of silica filler, compositions lose shape retention ability so that it becomes difficult to work or deal with the silicone rubber for processing or molding. Also they experience an extreme drop of physical properties such as tensile strength and tear strength. Conventional low hardness silicone rubber compositions are thus difficult to produce. Add Teflon powder to silicone rubber compositions to compensate for a reduction of the silica filler in order to secure shape retention is known although poor dispersion of Teflon powder is a problem.